1. Field of the Invention
The present invention relates to a ceramic composition to be made into a microwave ceramic dielectric, more particularly, to a ceramic composition to be made into a microwave ceramic dielectric which has a high Q value, a high relative permittivity, and a temperature coefficient permissible to practical use, and also exhibits its good quality invariably regardless of the firing temperature. The microwave ceramic dielectric will be used for dielectric resonators in the microwave frequency region, microwave IC substrates, and impedance matching of microwave circuits.
2. Prior Art
There is known a ceramic composition for a microwave ceramic dielectric (simply referred to as a dielectric ceramic composition hereinafter) which is composed of BaO, Nd.sub.2 O.sub.3, and TiO.sub.2 (as disclosed in Japanese Patent Laid-open No. 79753/1988). It has a disadvantage of being limited in the range of optimum firing temperature. In other words, it varies in characteristic properties (such as relative permittivity .epsilon.r, temperature coefficient of resonant frequency .tau.f, and Q value) depending on the firing temperature even though it has the same composition. This makes it difficult to obtain products of uniform quality. Moreover, it has a little high temperature coefficient of resonant frequency, i.e., +10 to 20 ppm/.degree.C., whereas the desirable value is in the neighborhood of 0 ppm/.degree.C.